Copper deficient Zn–Cu–In–Se quantum dot sensitized solar cells for high efficiency

Abstract

Improving the intrinsic optoelectronic properties of quantum dots (QDs) is essential to tap their potential as light-harvesting materials in QD sensitized solar cell (QDSC) applications. High quality composition controllable Zn–Cu–In–Se (ZCISe) QDs were synthesized, and the influence of non-stoichiometry on the optoelectronic properties, as well as on the photovoltaic performance of the resulting QDSCs, was investigated systematically. Experimental results revealed that the Cu content in the ZCISe QDs can remarkably influence the optical properties of QDs as well as the resultant photovoltaic performance of solar cells. The power conversion efficiency (PCE) can be distinctly improved with the use of Cu-deficient ZCISe QDs as a sensitizer regardless of the compromised light harvesting capability. Transient absorption (TA) and open-circuit voltage decay (OCVD) measurements demonstrated that the defect state-related donor–acceptor pair (DAP) in the ZCISe QDs was favorable for the enhancement of the lifetime of photogenerated electrons in the ZCISe QDSCs. The long-lived electrons in the Cu-deficient ZCISe QDs benefit the improvement of the photovoltaic performance of the resultant cell devices by suppressing charge recombination. Electrochemical impedance spectroscopy (EIS) results illustrated that the charge recombination process at the photoanode/electrolyte interfaces can be effectively inhibited in Cu-deficient ZCISe QD based cells. Finally, a highest PCE of 12.57% (J_sc = 25.97 mA cm⁻², V_oc = 0.752 V and FF = 0.644) was achieved employing ZCISe QDs with a Cu/In molar ratio of 0.7 under AM 1.5 G one full sun illumination. This is one of the highest efficiencies in QDSCs.